We have a substance. We study it using physical methods and determine that its molecules have a dipole moment , they are polarized under the action of an external electromagnetic field ... We determine the structure of the molecule. We compare with other molecules and come to the conclusion that in some molecules the electron density shifts under the action of a magnetic field along a chain of sigma bonds (inductive effect). For other molecules, the electron density shifts along the chain of pi bonds (resonant effect). Bonds between atoms in molecules are primary, while inductive and resonant effects are secondary.